The UK airport that I worked at - or maybe it was just the company that I worked for - you didn't necessarily need a clean license when starting employment (some events were okay, some were not), but if you acquired 'points' throughout the year and got to the 'magic 12', then you automatically lost your ADP.
Once a year we were asked to give our driving licenses to 'the management' who'd take a copy and date it; this then served as evidence that on the given date you had 'X' points. If you had 12 or more points then your ADP was summarily withdrawn, and you either worked elsewhere, or lost your job.
On one occasion ... somebody got summonsed for speeding and knew he'd get 'points', but that would take him over the '12'. A week before his court case he presented his DL to the Boss showing 9 points. A week later he had 6 points added, and lost his license. He kept quiet about it, took the bus to work, but kept on driving airside at work.
One year later, when asked to re-present his license, some of his original 9 points had elapsed, and he was back below 12 again (just!). The Boss was not too impressed! and gave him a hard time; eventually Management sacked him!
The moral of this ... don't try to be too clever, as you will always be found out.